1. Field of the Invention
The invention relates to a method and apparatus for on-the-spot sampling of small amounts of fluid for analysis. More particularly, it relates to a disposable device that operates by a combination of capillary action to collect a small fluid sample (such as blood), and by pressure differential when inserted into an analyzer to move the fluid into and out of a test chamber, exposing the fluid sample for testing by an analyzer.
2. Discussion of the Background
Physicians routinely test blood parameters as part of the diagnostic process. The complete blood count (CBC) is the most common of these tests. Physicians use the results to assess the quantity and the condition of the blood's cellular components. Three of the elements of the complete blood count are used to describe the size and number of red blood cells in the sample: the hematocrit (HCT), the mean corpuscular volume (MCV), and the red blood cell count (RBC). Four more blood properties describe the oxygen-carrying capacity of the red blood cells: the hemoglobin concentration (HGB), total protein concentration (TPC), the mean cellular hemoglobin (MCH), and the mean cellular hemoglobin concentration (MCHC).
These blood properties, in particular HCT or HGB, can be used to diagnose anemia, acute blood loss, dehydration, and scores of other conditions. HCT or HGB can also be used to assess the oxygen carrying capability of the blood.
In the hospital environment, medical personnel typically collect blood samples and then transfer the sample to a central blood lab for analysis. Two well-known methods of collecting blood samples include: (1) collecting the sample into a capillary tube following a finger, heel, or earlobe stick, and (2) collecting the blood sample into a vial using a syringe. Capillary tubes are made of glass or hydrophilic plastic open at both ends. One end of the tube is placed against the site of a small incision on the finger, heel, or ear lobe, and blood flows into the tube from the incision by capillary action. In either case the capillary tube or vial containing the blood sample is delivered to the lab where an automated system performs the testing.
Recently, research and development in the area blood collection and testing has been conducted in light of: (1) the risks associated with transfer of blood between containers including contamination of the blood sample and the increased risk to medical or laboratory personnel of exposure to blood-borne communicable diseases, such as hepatitis B, hepatitis C, and HIV; and, (2) the need and desire for accurate on-the-spot analysis of blood samples in emergency situations, blood banks, or in office or home environments. As a result, a variety of portable blood analyzers have been developed which are capable of taking optical, electrical conductivity or ultrasonic readings of a blood sample in order to measure blood components and characteristics such as hematocrit, hemoglobin, mean corpuscular volume, red blood cell count, mean cellular hemoglobin, mean cellular hemoglobin concentration, and total protein concentration. These portable blood analyzers have in turn engendered a need for a single-use disposable device that serves as a collection receptacle, temporary storage container, and testing chamber for blood samples to be used in conjunction therewith.
The general concept of a disposable blood sample collector, which uses capillary action to draw blood from the site of a finger stick or the like, and then transfers the blood to another container or chamber within the same device for centrifuging, is known. The following prior art references illustrate this concept. U.S. Pat. No. 4,314,570 to Sarstedt discloses a disposable blood sample collector and storage receptacle having a short capillary tube communicating with a somewhat larger chamber. The chamber is filled, the capillary tube is disconnected, and the chamber containing the blood sample is placed in a centrifuge or tested directly. U.S. Pat. No. 5,472,671 to Nilsson et al. discloses a two cavity blood sample collection device. A blood sample is collected into the first cavity by capillary action and may be mixed with a reagent. The blood sample is then transferred by centrifugal force through a channel into a second cavity. Different reactions/analyses can be carried out in the different cavities. U.S. Pat. No. 5,916,814 to Kenney discloses a pre-sealed integral hematocrit test assembly. The assembly essentially comprises a holder for holding together both a blood sample tube and hematocrit test tube during centrifugation, whereby the blood from the sample tube is funneled into the test tube and separated into columns.
Additional devices, which are designed for both collection and testing (other than centrifuging) of blood, are also known. For example, typical home-use blood glucose monitors involve the user inserting a test strip into a monitor, lancing their finger, squeezing out a drop of blood, aiming the drop of blood so that it lands on the small test surface of the test strip. U.S. Patent Application 2003/0007893 of Purcell discloses a testing device for on-the-spot blood glucose monitoring (i.e. by photometric, colorimetric or electrochemical analyzers) that attempts to ensure that the user collects the necessary volume of blood with minimal air bubbles. Purcell developed an elongated test sensor insertable into a monitor. The sensor has a higher volume pick-up area at one end and a lower volume read area at the other. The read area end is inserted into the monitor. A blood sample from a finger stick is dripped onto and collected in the pick-up area of the test sensor. If the pick-up area volume is filled, an amount of blood required for testing will necessarily flow by capillary action through a transfer area and into a read area containing a reagent, where the monitoring unit reads the results. A cover over the transfer and read areas protects the monitoring unit.
Lastly, the concept of transferring a fluid sample from a collection area to a testing area within a device using a pressure differential is known. U.S. Patent Application 2003/0118479 of Quirk et al. discloses a device that is attached and sealed to a removable test strip (coated with a reagent) forming a testing chamber into which a collected blood sample can be directed towards or away from by inducing a pressure differential on the sample.
None of the above devices provide an all-in-one disposable device that collects and temporarily safely stores a blood sample for analysis, and which is insertable into the testing region of a portable analyzer to thereby seal the testing surfaces, forming a sealed testing chamber, and which incorporates or interfaces with an actuator which initiates a pressure differential to move the blood sample into and out of the testing chamber. The unique structure of this device used in conjunction with an analyzer provides a quick, clean and safe way of collecting and testing a predefined amount of blood (or other fluid), especially in emergency or non-laboratory settings.